1. Field of the Invention
This invention relates generally to cameras, and more particularly is directed to cameras of the type having a camera body on which exchangeable lens devices are interchangeably mountable.
2. Description of the Prior Art
It has been proposed to provide a video or other camera comprised of a main portion or camera body on which exchangeable lens devices are interchangeably mounted so that, at any time, the lens device in use will be best suited for the encountered conditions.
It has further been proposed, in such cameras, to detect optical information within the camera body, such as, the focused condition of, or the amount of light in an image projected by the exchangeable lens device onto an imaging element within the camera body, and to control functions of an imaging lens assembly included in the exchangeable lens device on the basis of such optical information, for example, so as to effect so-called auto focusing and/or automatic exposure control. In order to achieve such automatic control of functions of the imaging lens assembly, sensors are provided within the camera body for sensing the optical information, whereupon a drive voltage based on the sensed optical information is supplied to the exchangeable lens device for operating a drive motor or the like by which a function of the imaging lens assembly, such as, the focusing or exposure, is automatically adjusted, for example, as in U.S. Pat. No. 4,609,944 and U.S. Pat. No. 4,471,383, respectively, which each have a common assignee herewith.
In the previously proposed camera in which a drive voltage is supplied from the camera body to the exchangeable lens device for operating a drive motor in the latter by which a respective function of the imaging lens assembly is adjustably controlled, it is necessary to provide a current conducting path, including respective electrical contacts at an interface between the camera body and the exchangeable lens device, for each of the several adjustable functions of the imaging lens assembly, for example, for the auto focusing and automatic exposure control functions. Therefore, as the number of automatic functions is increased, the number of current conducting paths or channels between the camera body and the exchangeable lens device has to be correspondingly increased leading to increased size and cost of the camera. Further, the characteristics of the drive motors included in the several exchangeable lens devices intended to be used interchangeably with one camera body may be substantially unequal by reason of differences in the focal lengths or weights of the imaging lens assemblies included in the exchangeable lens devices, respectively. This makes it difficult to effect the optimum control of the imaging lens assemblies of the interchangeably used lens devices by means of the drive voltages produced in the camera body without reference to the characteristics of the exchangeable lens device then mounted thereon.